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Slow Growing Embryo? Likely a GIRL!

Faster growing embryos resulted in more male births and slower growing embryos resulted in more females

It was found that if you transfer an embryo that has a total number of cells less than the mean in the total number of embryos, then there is a very large increase in the number of female births (88.8% of births being female). If in fact you transfer an embryo that has a number of cells greater than that mean in the total number of embryos available for transfer, then the situation is reversed and you observe 90% of offspring being male.

Tarrin et al(1995) have discussed whether in fact in vitro selection programs carried out around the world may in fact be inadvertently affecting the ratio of female to male babies. In this study, three groups of IVF patients were described based on the number of cells present in the embryo transferred relative to the mean number of cells in all embryos that were ready for transfer. It was found that if you transfer an embryo that has a total number of cells less than the mean in the total number of embryos, then there is a very large increase in the number of female births (88.8% of births being female). If in fact you transfer an embryo that has a number of cells greater than that mean in the total number of embryos available for transfer, then the situation is reversed and you observe 90% of offspring being male.

So by selecting for fast cleaving embryos, those that have high numbers of cell divisions, and slow cleaving embryos, those that have a low number of cell divisions, it is possible to affect the sex ratios in the subsequent offspring (Tarrin et al, 1996). A second finding is that in fact maternal age has an effect on the ratio of male to female offspring. It was found that in patients below 35 years of age, 62.7% of births were males and in patients above 35 years of age 71.4 were female. So clearly these results would suggest that by selecting slow cleaving(slow dividing) and rapidly cleaving( fast dividing) embryos and by maternal age, it is actually possible to affect the ratio of female to male babies born through in vitro fertilization.